Effect of substrate temperature on the characteristics of α-MoO3 hierarchical 3D microspheres prepared by facile PVD process

The authors report the fabrication of morphologically controlled α-MoO3 hierarchical microspheres (MSs) with the nanoflakes (NFs) on nickel coated glass substrate using a facile low cost physical vapor deposition (PVD) routes without any template or surfactant. The synthesis mechanism of MSs includes the sequences of plasma assisted sublimation and thermal evaporation processes in three independent steps. It is experimentally demonstrated that the nanostructured thin film with vertically aligned NFs during first growth step provides a seed layer for the growth of MSs. The morphological, structural, and optical properties of MoO3 MSs are investigated systematically as function of substrate/growth temperatures. The obtained results endorse the surface morphology of α-MoO3 MSs are strongly depending on the growth temperature at the final growth step. HRTEM analysis with SAED assured that NFs existing on the surface of MoO3 MSs are single crystalline in nature. The vibrational study of molybdenum and oxygen atoms in MSs is carried out by micro-Raman and infra-red (IR) spectroscopy, which evident the presence of single orthorhombic phase of MoO3 MSs and agreed with XRD results. The MoO3 MSs exhibit photoluminescence (PL) in the UV-visible region at room temperature and the emission is observed to be strongly enhanced with the increase of substrate/growth temperature in accordance with the improvement in the degree of crystallinity characterized by XRD analysis.